Apparatus and method of controlling the thermal performance of an oxygen-fired boiler

ABSTRACT

A method of controlling the operation of an oxy-fired boiler includes combusting a fuel that comprises oil heavy residues in a boiler, the oil heavy residues including hydrocarbon molecules having a number average molecular weight from approximately 200 to approximately 3000 grams per mole, discharging flue gas from the boiler, recycling a portion of the flue gas to the boiler, combining a first oxidant stream with the recycled flue gas to form a combined stream, splitting the combined stream into a plurality of independent split streams, introducing each independent split stream at a different elevation of the boiler, and controlling independently a parameter of each of the independent split streams to adjust the heat release at each respective elevation of the boiler to vary the heat release profile of the boiler by adding a second oxidant stream to each respective independent split stream to form respective independent oxygen enriched split streams.

CROSS-REFERENCE

This Application is a Continuation-in-Part of U.S. patent applicationSer. No. 13/298,147, filed on Nov. 16, 2011, which claims the benefit ofU.S. Provisional Application Ser. No. 61/414,175, filed on Nov. 16,2010, both of which are hereby incorporated by reference herein in theirentireties.

BACKGROUND

Technical Field

This disclosure relates generally to oxy-fired boilers, and morespecifically to an oxy-fired boiler that burns heavy oil residues asfuel.

Discussion of Art

Oxy-combustion has been developed for carbon dioxide capture andsequestration in fossil fuel fired power plants. The concept ofoxy-combustion (also sometimes referred to as ‘oxyfuel’ and‘oxy-firing’) is to replace combustion air with a mixture of oxygen andrecycled flue gas, thereby creating a high carbon dioxide content fluegas stream that can be more simply processed for sequestration. Asimplified exemplary schematic of the oxy-combustion process forpulverized coal (pc) power plants is shown in prior art depicted in FIG.1.

FIG. 1 depicts an oxy-combustion system 100, comprising an airseparation unit 102, a boiler 104, a pollution control system 106 and agas processing unit 108. The air separation unit 102 is located upstreamof the boiler 104, which is located upstream of the pollution controlsystem 106 and the gas processing unit 108. The pollution control system106 is located upstream of the gas processing unit 108. Gas recycle isshown taken after the pollution control system, but could be taken fromany location between the boiler and the gas processing unit.

The boiler 104 may be a tangentially fired boiler (also known as aT-fired) or a wall fired boiler. T-firing is different from wall firingin that it utilizes burner assemblies with fuel admission compartmentslocated at the corners of the boiler furnace, which generate a rotatingfireball that fills most of the furnace cross section. Wall firing (notshown), on the other hand, utilizes burner assemblies that areperpendicular to a side (of the shell) of the boiler.

FIG. 2 depicts a tangentially fired boiler 104. Tangentially firedboilers have a rectangular cross-section and have burner assemblies 105positioned at the corners. Fuel and transport air are introduced intothe boiler 104 via the burner assemblies 105 and are directedtangentially to an imaginary circle located at the center of the furnaceand with a diameter greater than zero. This generates a rotatingfireball that fills most of the furnace cross section. The fuel and airmixing is limited until the streams join together in the furnace volumeand generate a rotation. This has often been described, as “the entireboiler is the burner.” Global boiler aerodynamics and mixing is muchmore important to the combustion process and the resulting boilerperformance during T-firing as compared with wall-firing. Duringwall-firing, fuel and air/oxygen mixing occurs in or near the burnersand less mixing occurs in the boiler.

With reference now once again to FIG. 1, in one method of operating theoxy-combustion system 100, oxygen is first separated from nitrogen inthe air separation unit 102. The nitrogen is discharged separately fromthe air separation unit. The air separation unit 102 extracts oxygenfrom the atmosphere.

The oxygen is then discharged from the air separation unit 102 tocombine with recycled flue gas, the combination of which is fed to theboiler 104. The boiler 104 uses the oxygen present in the flue gasstream to combust a fuel (e.g., coal, oil, or the like) to generate heatand flue gases. As a result of combusting the fuel with oxygen insteadof with air, the flue gas produced has a high carbon dioxide content.The other constituents of the flue gas are water vapor and small amountsof oxygen, nitrogen, and pollutants such as sulfur oxides, nitrogenoxides, and carbon monoxide. Removing the water and other componentsproduces a very pure carbon dioxide stream suitable for sequestration orother use.

The heat is used to generate steam, which may be used to drive agenerator (not shown) to produce electricity, while the flue gases aredischarged to the pollution control system 106 where particulate matterand other pollutants (e.g., NOx, SOx, and the like) are removed. Aportion of the purified flue gases is recycled to the boiler 104 asshown in FIG. 1. The remaining flue gases (that substantially comprisecarbon dioxide) are discharged to the gas processing unit 108 from whereit is sequestered.

As will be readily appreciated, recycling large amounts of flue gases tothe boiler 104 require large. On the other hand, burning the fuel withpure oxygen generally produces flame temperatures much too high forpractical boiler materials, so a portion of the high-carbon dioxide fluegas is used to dilute the oxygen and moderate the boiler temperature.The amount of oxygen added to the recycled flue gas is based on theamount of fuel combusted in the boiler. The fuel uses a certain amountof oxygen in addition to some amount of excess oxygen to ensure completecombustion.

While most of the aforementioned discussion has been directed to theoxy-fired boilers that use coal for combustion, it is desirable to useother fuels, such as, for example, liquid fuels in oxy-fired boilers.

One such liquid fuel is oil heavy residue. Oil heavy residues compriseprimarily high molecular weight hydrocarbon products of crude oil thatmay be unsuitable for use in other applications or that cannot easily beconverted into lower molecular weight products that can be used in otherapplications. Oil refineries convert crude oil into a range of useableproducts (e.g., gasoline, diesel and fuel oil components) that are usedcommercially. The first step in the manufacture of petroleum products isthe separation of crude oil into the main fractions by atmosphericdistillation. When crude oil is heated, the lightest and most volatilehydrocarbons boil off as vapors first and the heaviest (i.e., thosehaving higher molecular weights) and least volatile last. The vapors arethen cooled and condensed back into liquids, which are then supplied forcommercial use.

The residue from atmospheric distillation is sometimes referred to aslong residue and to recover more distillate product, furtherdistillation is carried out at a reduced pressure and high temperature.Vacuum distillation is one such process and is used to further recoveruseful products from the long residue. The percentage of residue variesdepending on the composition of crude processed. For a typical “light”North African crude the residue is 28%, whilst for a “heavy” Venezuelancrude it is as high as 85%. The proportion of products produced does notalways match the product demand and is primarily determined by theparticular composition of crude oil.

Further refining such as thermal cracking at temperatures of 450 to 750°C. and pressures from atmospheric to 70 bar are used to convert the longresidue into useful commercial product. The temperature and pressuredepends on the type of feedstock and the product requirement. At theseelevated temperatures, the large hydrocarbon molecules become unstableand spontaneously break into smaller molecules. Several differentthermal cracking processes may be performed on the residues to convertthem to useful commercial products. However, not all of the highmolecular weight hydrocarbon molecules can be converted to lower weightmolecules that can be marketed commercially. The high molecular weighthydrocarbon molecules that are finally left behind after all of theuseful product is extracted for commercial use is called oil heavyresidue. It is desirable to find uses for the oil heavy residue thatcannot be used for conventional commercial products such as gasoline andfuel oil.

It is therefore desirable to use the oil heavy residue in oxy-firedboilers to reduce waste and to reduce the environmental impact byemploying these liquids in and efficient combustion processes that has avery low environmental signature as compared with other comparativecombustion processes.

BRIEF DESCRIPTION

In an embodiment, a method of controlling the operation of an oxy-firedboiler is provided. The method includes combusting a fuel that comprisesoil heavy residues in a boiler, the oil heavy residues includinghydrocarbon molecules having a number average molecular weight fromapproximately 200 to approximately 3000 grams per mole, discharging fluegas from the boiler, recycling a portion of the flue gas to the boiler,combining a first oxidant stream with the recycled flue gas to form acombined stream, splitting the combined stream into a plurality ofindependent split streams, introducing each independent split stream ata different elevation of the boiler, and controlling independently aparameter of each of the independent split streams to adjust the heatrelease at each respective elevation of the boiler to vary the heatrelease profile of the boiler by adding a second oxidant stream to eachrespective independent split stream to form respective independentoxygen enriched split streams.

In another embodiment, a method is provided. The method includes thesteps of combusting a fuel that comprises oil heavy residues in aboiler, where the oil heavy residues that comprise hydrocarbon moleculeshaving a number average molecular weight from 200 to 3000 grams permole, discharging flue gas from the boiler, recycling a portion of theflue gas to the boiler, combining a first oxidant stream with therecycled flue gases to form a first combined stream, splitting the firstcombined stream into a plurality of independent split streams, combininga second oxidant stream to each respective independent split streamprovided to the boiler to form respective independent oxygen enrichedsplit streams, introducing each independent oxygen enriched split streamto a different elevation of the boiler, and controlling independentlythe amount of the second oxidant stream added to each respectiveindependent split stream to adjust the heat release at each respectiveelevation of the boiler to vary the heat release profile of the boiler.The first combined stream, the independent split streams, and theindependent oxygen enriched split streams do not carry the fuel for theboiler.

In yet another embodiment, a system is provided. The system includes anair separation unit, a boiler configured to combust oil heavy residues,the oil heavy residues comprising hydrocarbon molecules having a numberaverage molecular weight from 200 to 3000 grams per mole, a pollutioncontrol system, a gas processing unit and a control system. The airseparation unit is upstream of the boiler, the pollution control systemand the gas processing unit. The boiler is upstream of the pollutioncontrol system and the gas processing unit. The control system isconfigured to control the addition of a first oxidant stream to therecycled flue gas to form a combined stream and to control the additionof a second oxidant stream to a plurality of independent split streamsformed from the combined stream to vary the heat release profile of theboiler. Each of the independent split streams to which the secondoxidant stream is added is introduced to a different elevation of theboiler.

DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 represents the prior art and depicts a combustion system whereflue gases are recycled to the boiler;

FIG. 2 depicts a prior art tangentially fired boiler;

FIG. 3 is a depiction of the various points at which a combined streamthat comprises a first oxidant stream (that comprises substantiallyoxygen) and a second stream (that comprises substantially recycled fluegases) can be introduced into the boiler;

FIG. 4 is another depiction of an exemplary embodiment of introducingoxygen into the flue gas stream into the boiler;

FIG. 5 represents a depiction of one embodiment of the introduction ofthe combined stream into a tangentially fired boiler;

FIG. 6 depicts one embodiment of nozzle orientation that is used for thecombustion of oil heavy residues in concentric firing boilers;

FIG. 7 depicts a nozzle for injecting highly concentrated oxygen streamsin a concentric firing system;

FIG. 8 is a graph that shows improved carbon burnout/carbon heat losswith oxygen enrichment in the fuel compartment during 15 MW testing; and

FIG. 9 is a graph that illustrations the impact of oxygen enrichment onheat flux to the furnace wall near the burner/windbox during 15 MWtesting.

DETAILED DESCRIPTION

Reference will be made below in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference characters usedthroughout the drawings refer to the same or like parts. Whileembodiments of the invention are suitable for use with a tangentiallyfired boiler, embodiments of the invention may also be utilized inconnection with any oxygen fired boiler, including an oxygen wall firedboiler.

Embodiments of the invention relate to an oxyfuel combustion system thatuses oil heavy residue (OHR) such as vacuum bottoms from petroleumrefineries or high asphaltene materials, for boiler applications toenhance thermal performance and reduce emissions. The method disclosedherein includes applying selective oxygen injection into oxidantstreams, into the furnace windbox and into over fire air (OFA) nozzlesto control combustion rate and furnace heat flux distribution. Featuresinclude local oxygen enrichment to promote combustion and to improve thegaseous environment near the waterwall tubes to reduce corrosion.Features also include options for injection through special oxygensub-compartments through the burner/windbox into the furnace allowingmore of the windbox and associated equipment to be fabricated from lowercost material such as carbon steel.

As used herein, “oil heavy residue” refers to primarily high molecularweight hydrocarbon products of crude oil that may be unsuitable for usein other applications or that cannot easily be converted into lowermolecular weight products that can be used in other applications. Theoil heavy residues have number average molecular weights of 200 to 3,000grams per mole and comprise primarily hydrocarbon molecules. Substitutedand unsubstituted hydrocarbon molecules may be used. In an embodiment,the oil heavy residues comprise heavy oils, oil sands, bitumen,biodegraded oils, and the like, some of which may contain asphaltene.Asphaltenes are molecular substances that are found in crude oil, alongwith resins, aromatic hydrocarbons, and saturates (i.e., saturatedhydrocarbons such as alkanes). Asphaltenes consist primarily of carbon,hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts ofvanadium and nickel. The carbon to hydrogen (C:H) ratio is approximately1:1.2, depending on the asphaltene source. Asphaltenes are definedoperationally as the n-heptane (C₇H₁₆)-insoluble, toluene(C₆H₅CH₃)-soluble component of a carbonaceous material such as crudeoil, bitumen, or coal. Asphaltenes generally have a distribution ofmolecular weight in the range of 400 to 1500 grams per mole.

In an embodiment, the method includes varying the amount, proportionand/or distribution of oxygen, the amount, proportion and/ordistribution of recycled flue gases, or both the amount, proportionand/or distribution of both oxygen and recycled flue gases in a combinedstream that is fed to various inputs to the boiler, an input streamprovided to the boiler and/or various zones of the boiler. For example,the volume of oxygen sufficient for the desired amount of combustion ofthe fuel provided to the boiler in accordance with desiredstoichiometric parameters may be portioned or distributed to differentzones or locations of the boiler to provide a desired heat releaseprofile in the boiler. Further, the recycled flue gas and/or volume ofoxygen may be proportioned and/or distributed to different areas withina zone of the boiler to provide a desired heat release profile in thatzone. Furthermore, the proportion and/or distribution of addition of avolume or proportion of oxygen and/or recycled flue gas to an inputstream to the boiler may be controlled to provide a desired heat releaseprofile.

In one embodiment similar to that shown in FIG. 3, a system and methodincludes supplying a first combined stream of recycled flue gas and afirst oxidant stream to different sections or zones of the boiler. Thefirst combined stream may be supplied to a hopper zone, the windbox zoneand/or one or more overfired oxidant compartments at different volumes,which are each controlled by a respective fluid flow control device. Inthis embodiment, the ratio of oxygen to the recycled flue gas isconstant in any of the zones of the boiler to which it is introduced,however, the distribution of the first combined stream is controlled byproviding varying portions of the first combined stream to differentzones of the boiler and/or different locations within a particular zoneto provide a desired heat release profile.

In another embodiment similar to that shown in FIG. 4, a system andmethod comprises combining the first combined stream with a secondoxidant stream to form a second combined stream that may be supplied tothe boiler at the hopper zone, the windbox zone and/or one or moreoverfired oxidant compartments at different volumes amounts, wherein thevolumetric flow of the second oxidant is controlled by a fluid flowcontrol device. This method of enriching the first combined stream isconducted just prior to the introduction of the second combined streaminto the boiler. In this system and method, the amount of oxygen to thehopper zone, the windbox zone, the hopper zone and/or the overfiredoxidant compartments is varied relative to the amount of the recycledflue gas. This system and method can be advantageously used to vary theheat release pattern in the boiler.

This system and method of controlling the distribution of oxygen and/orrecycled flue gas to the boiler is advantageous in that it permitslocalized oxygen enrichment of the atmosphere in the boiler and henceincreasing the localized heat release and modifying the temperatureprofiles in desired areas of the boiler.

In yet another embodiment similar to that in FIGS. 3 and 4, the amountof flue gas in the combined stream may be varied instead of or inaddition to varying the amount of the oxygen. In yet another embodiment,the invention details modulating or changing the proportion ordistribution of the recycled flue gas admitted to the boiler at varyingelevations relative to the furnace outlet plane. This method ofcontrolling the flow rates of flue gases is advantageous in that itallows for maintaining a constant steam temperature control as fuelproperties or furnace conditions vary. This provides a means of steamtemperature control as loads vary. Another method of steam temperaturecontrol can be achieved by modulating the amount of oxygen to thevarying elevations.

An advantage of the present invention the amount of oxygen and flue gasprovided to a fluid stream in an oxygen fired boiler may beindependently controlled to provide great flexibility to optimize theoperation of the boiler and provide or modify the heat release profileof the boiler. One skilled in the art will appreciate that an increaseof oxygen with an input fluid stream to the boiler will result in anincrease heat flux at the location of the input fluid stream.

FIG. 3 is a depiction of a boiler 200, such as a T-fired boiler, havinga control system 290 that controls the proportion or distribution of acombined stream 320 to various locations or zones of the boiler. Thecombined stream 320 comprises a first oxidant stream 310 (that comprises0-100 weight % of oxygen, wherein in one embodiment stream 310 issubstantially oxygen) and a second stream 350 (that comprisessubstantially recycled flue gases). The volumetric flow of the firstoxidant stream 310 and second stream 350 are controlled by respectivefluid flow control devices 311, such as baffles, fans, dampers, valves,and eductors. These flow control devices may be controlled in an openloop or closed loop control system, which will be described in greaterdetail hereinafter.

The oxidant is injected into three main zones (all of which are detailedbelow): 1) a windbox/main burner zone, where it is injected at thelowest stoichiometric ratio of flue gas to oxygen, (2) a furnace locatedabove the windbox (also termed an over-fire zone), where thestoichiometric ratio of flue gas to oxygen is more than 1; and 3) afurnace hopper located below the windbox.

The bulk of the oxygen for combustion is injected and mixed into themain gas recirculation flow taken from after a pollution control system(not shown) to form a premix oxidant 320 which is heated in aregenerative gas-gas heater 390 and sent to the windbox and over fireair system. The total quantity of flue gas recirculation is establishedbased on the size and heat transfer surfacing of the boiler.

With reference again to the FIG. 3, the boiler 200 includes a hopperzone 210 located below the main burner zone 208 from which ash can beremoved, a main burner zone 208 (hereinafter windbox 208) where anoxidant and an oxidant-fuel mixture (or alternatively a gas-fuelmixture) is introduced into the boiler 200, a burnout zone 216 where anyoxygen or fuel that is not combusted in the main burner zone getscombusted, a superheater zone 212 where steam can be superheated, and aneconomizer zone 214 where water can be preheated prior to entering thesuperheater zone 212. The burnout zone 216 can utilize a lower overfiredoxidant compartment 206 and an upper overfired oxidant compartment 204.The boiler 200 also includes a horizontal boiler outlet plane 304 and avertical boiler outlet plane 302. The boiler 200 also includeswaterwalls 202 in which the water is transformed to steam.

As noted above, a first oxidant stream 310 and a second stream 350 arecombined to form the combined stream 320 that is then fed to the boiler.The combined stream 320 can comprise about 15 to about 40 volume percentoxygen, with the remainder being recycled flue gases. As can be seen inFIG. 3, the combined stream 320 can be fed to the boiler 200 into thehopper zone 210, into the windbox 208, into the lower overfired oxidantcompartment 206 and/or into an upper overfired oxidant compartment 204.In other words, the combined stream 320 can be split up and distributedinto several split streams (320A, 320B, 320C and/or 320D) and fed intodifferent parts of the boiler to vary the heat release profile in theboiler and to improve its thermal performance, whereby the volumetricflow rate of one or more of the split streams 320A, 320B, 320C, 320D iscontrolled by a respective fluid flow control device 312. For example ahigher percentage of the combined stream 320 may be provided to thewindbox 208 to increase the heat release profile in this zone, or viceversa. This method of enriching the second stream 350 with oxygen andsplitting the combined stream 320 into different streams 320A, 320B,320C, 320D permits varying the amount of flue gas and oxygen intodifferent parts of the boiler to improve its thermal performance orprovide a desired heat release profile.

For purposes of identification, the combined stream 320 that is fed intothe boiler 200 at the hopper zone 210 is identified as 320A and cancomprise up to about 25 weight percent of the total weight of thecombined stream 320. In one embodiment, the combined stream 320A streamcan comprise about 0 to about 10 weight percent of the total weight ofthe combined stream 320. In another embodiment, the combined stream 320that is fed into the boiler 200 at the windbox zone 208 is identified as320B and can comprise about 50 weight percent to about 100 weightpercent of the total weight of the combined stream 320. In oneembodiment, the combined stream 320B stream can comprise about 50 toabout 80 weight percent of the total weight of the combined stream 320.In yet another embodiment, the combined stream 320 that is fed into theboiler 200 at the lower overfired oxidant compartment 206 is identifiedas 320C and can comprise up to about 50 weight percent of the totalweight of the combined stream 320. In one embodiment, the combinedstream 320C stream can comprise about 10 to about 30 weight percent ofthe total weight of the combined stream 320.

In yet another embodiment, the combined stream 320 that is fed into theboiler 200 at the upper overfired oxidant compartment 204 is identifiedas 320D and can comprise up to about 50 weight percent of the totalweight of the combined stream 320. In one embodiment, the combinedstream 320D stream can comprise about 10 to about 30 weight percent ofthe total weight of the combined stream 320.

FIG. 4 depicts another embodiment of a boiler 200, such as a T-firedboiler, having a control system 291 that controls the proportion ordistribution of a combined stream 360 and the oxygen ratio of each splitstream 360A, 360B, 360C, 360D to various locations or zones of theboiler, using a combined stream 360 and a second oxidant stream 370 toenrich or deplete the flue gas of oxygen of each respective input streamsupplied to the boiler 200 to define or vary the heat release profile inthe boiler and to improve its thermal performance or provide a desiredheat release profile.

The control logic for a boiler that burns oil heavy residues requirescontrolling the specific oxygen concentrations to predetermined valuesfor each of the three main furnace zones—the oxidant compartments 204and 206, the windbox zone 208 and the hopper zone 210. This includescontrolling oxygen flow rates and oxygen concentrations in each splitstream 360A, 360B, 360C, and 360D as well any further subdivisions ofthese streams (not shown here). The flow rate and oxygen concentrationof each of the streams is adjusted to provide a final value based on theoxygen concentration in the flue gas leaving the boiler in order tomaintain the optimize amount of oxygen efficient combustion.

The distribution of this oxygen into the furnace is specificallyoptimized in dependence upon the specific composition and properties ofthe oil heavy residue fuel and the design of the boiler. Control of theoxygen added to specific oxidant or flue gas recirculation streamsprovides a means to control combustion rate and heat release allowingcontrol of furnace heat flux profiles and steam temperature control.Moreover, it provides a means to optimize and improve combustionperformance including flame stability/turndown and carbon burnout. Italso provides a means to improve combustion performance allowing moreaggressive staging for NOx control and lower NOx emissions.

In an embodiment, streams having different oxygen concentrations are fedto the hopper zone 210, the windbox zone 208, the upper overfiredoxidant zone 204 and the lower overfired oxidant zone 206. One skilledin the art will appreciate that the control oxygen concentration orratio of each zone may be controlled in any configuration or combinationof locations or zones of the boiler. The recycled flue gases 350 may befirst pre-mixed with an oxidant stream 310 to form a first combinedstream 360. The first combined stream 360 is then discharged towardsdifferent locations or zones of the boiler in different amounts orvolumes. However, each combined stream 360 is enriched with oxygen froma respective second oxidant stream 370 to provide each respective input(split) stream 360A, 360B, 360C, 360D with the desired concentration ofoxygen as well as the desired overall volumetric flow for each inputstream. The ratio of oxygen in the different split streams can thereforebe the same or different from one another.

As shown in FIG. 4, the control system 291 controls the concentration ofoxygen and volumetric flow of the combined stream 360 by controlling thefluid flow of stream 350 and oxidant stream 310 using the respectivefluid flow control devices 311. The control system 291 further controlsthe concentration of oxygen and volumetric flow rate for each respectiveinput stream 360A, 360B, 360C, 360D by controlling the respective fluidflow control devices 312 to control the flow of the combined stream 360and controlling respective fluid flow control devices 313 to control theflow of respective fluid flow control devices 313. The fluid flowcontrol device 312 may be disposed upstream or downstream of the pointthat the second oxidant stream 370 is added. However, when the fluidflow control device 312 is disposed upstream of the point that thesecond oxidant stream 370 is added, the control system 291 providesgreater flexibility and concentration range to locally control both theconcentration of oxygen and the overall volume of input stream 360A,360B, 360C, 360D to the boiler. In summary as shown in FIG. 4, the fluidflow control devices 311, 312, 313 of the control system 291 can controlthe oxygen concentration of each input stream 360A, 360B, 360C, 360D thedistribution of oxygen to each input stream and thus zone of the boiler,and the desired volumetric gas flow of each input stream.

With reference once again to FIG. 4, a first oxidant stream 310 of thetotal added oxygen is mixed with a second stream 350 that comprisesrecycled flue gases to form a first combined stream 360. In an exemplaryembodiment, the first oxidant stream 310 comprises about 50 to about 95percent of the total added oxygen, specifically about 80 to about 90percent. The remaining percentage of oxygen necessary for the desiredamount of combustion in the boiler 200 is provided in the second oxidantstream 370. Note that the recycled flue gas and the transport gas mayinclude a small percentage of oxygen that may need to be considered inthe control of the input streams 360A, 360B, 360C, 360D.

As can be seen in FIG. 4, the second combined stream 360A whichcomprises the first combined stream 360 and the second oxidant stream370 comprising up to 20% of the total added is fed to the hopper zone210. In an exemplary embodiment, the second combined stream 360A cancomprise about 0 to about 18%, and more specifically about 2 to about15% of the total added oxygen.

In another embodiment, a second oxidant stream 370 that comprises oxygenin an amount of up to 100% of the total added oxygen is combined withthe first combined stream 360 and fed to the windbox 208. In anexemplary embodiment, the second oxidant stream comprises oxygen in anamount of about 50 to about 80% of the total added oxygen is combinedwith the first combined stream 360 and fed to the windbox 208.

In yet another embodiment, a second oxidant stream 370 that comprisesoxygen in an amount of up to 50 wt % is combined with the first combinedstream 360 and fed to the lower overfired oxidant compartment 206. In anexemplary embodiment, the second oxidant stream comprises oxygen in anamount of about 10 to about 30% of the total added oxygen is combinedwith the first combined stream 360 and fed to the lower overfiredoxidant compartment 206 and/or to the upper overfired oxidantcompartment 204.

The second oxidant stream 370 is generally mixed with the first combinedstream 360 to form the combined stream 360A, 360B, 360C or 360D as closeas possible to the boiler 200. A finer level of control over oxygendistributions can be achieved by mixing in oxygen closer to the boiler,for example adding additional oxygen at the positions depicted in FIG. 4to locally enrich the oxygen content in one area of the windbox 208.This mode of enrichment of the first combined stream 360 can be used inthe tangentially fired boilers as well as in wall fired boilers.

While the control systems 290, 291 of FIGS. 3 and 4 control thedistribution and concentration of oxygen to particular zones of theboiler 200, the present invention contemplates that each zone having aplurality of separate input streams may also be controlled by thecontrol systems. FIG. 5 depicts one exemplary apparatus and method ofintroducing the combined stream 320B (from FIG. 3) or 360B (from FIG. 4)into the windbox 208 of the boiler 200. FIG. 5 illustrates the detailsof the input compartments or input streams of a windbox 208 of atangentially fired boiler, and the apparatus and method of controllingthe oxygen concentration and volumetric flow of respective input streamsprovided by the windbox 208. Varying oxygen concentrations areintroduced in different compartments of the windbox 208.

FIG. 5 depicts a plurality of assemblies, e.g. primary nozzles 402, 404,406, in the windbox 208 of a tangentially fired boiler 200. FIG. 5contains an expanded view of the windbox 208 of the boiler 200 toillustrate a configuration of the nozzles 2 a through 2 k of nozzleassemblies 402, 404, 406. In one embodiment, the windbox 208 cancomprise about 2 to about 10 such assemblies of nozzles. It is to beappreciated that a number of different configurations between thenozzles that introduce the combined stream 360B, and those that deliverheavy oil residues to the windbox and those that deliver auxiliary airto the windbox may be used.

Oil heavy residue and transport gas, along with a mixture of recycledflue gas and oxygen (e.g., the combined stream 360B or 320B) can beintroduced into the respective nozzles. As can be seen in the FIG. 5,nozzles that supply the fuel to the windbox 208 may be alternated withnozzles that supply a mixture of recycled flue gas and oxygen to thewindbox. Further nozzles that supply auxiliary air may also bealternated with nozzles that supply recycled flue gas and oxygen to thewindbox.

The nozzles can be arranged into assemblies. For example, a first nozzleassembly 402 can contain a first nozzle that introduce the combinedstream 360B, a second nozzle that introduces the oil heavy residue and athird optional nozzle that introduces auxiliary air. A second nozzleassembly 404, a third nozzle assembly 406, and so on may be arranged ina similar fashion to the first nozzle assembly 402 in order to introducethe combined stream 360B, the oil heavy residue and the auxiliary airinto the windbox 208. It is to be noted that the second and third nozzleassemblies may alternatively have different configurations from thefirst nozzle assembly 402, if desired.

In an embodiment, it is desirable to introduce the combined stream 360B(with localized oxygen enrichment) into the nozzles 2 a, 2 c, 2 e, 2 g,2 i and 2 k respectively, while nozzles 2 b, 2 f, and 2 j deliver oilheavy residues to the windbox 208. In an embodiment, auxiliary air issupplied to the windbox 208 via nozzles 2 d and 2 h. From FIG. 5 it maytherefore be seen that the first nozzle assembly 402 contains thenozzles 2 a, 2 b, 2 c and 2 d, while the second nozzle assembly 404contains nozzles 2 e, 2 f, 2 g and 2 h, and third nozzle assembly 406contains nozzles 2 i, 2 j, 2 k, and so on.

The ratio of oxygen to the recycled flue gas in the combined stream 360Bthat is fed to the respective assemblies 402, 404, and so on can bevaried similar to the configuration shown and described in FIGS. 3 and4. Specifically, control systems 290, 291 of FIGS. 3 and 4 may have thesame configuration of fluid flow control devices to control theconcentration, proportion and/or distribution of each respective splitinput stream that feeds into each nozzle 2 a, 2 c, 2 e, 2 g, 2 i and 2k. In other words, the locations of nozzles (i.e., windbox zones) of thewindbox 208 may be controlled in the same or similar manner as each zoneof the boiler 200, whereby the input stream 360B would be functionallythe same as the combined stream 360 in FIGS. 3 and 4. While thisfunctionality has been shown for the windbox 208, one will appreciatethat this level of control is contemplated by the invention for otherzones of the boiler 200.

For example, the first nozzle 2 a can receive a first ratio of oxygen torecycled flue gases, while the second nozzle 2 c can receive a secondratio of oxygen to the recycled flue gases, and so on. In oneembodiment, the first ratio can be the same as the second ratio. Inanother embodiment, the mass ratio of the combined stream 360B to theoil heavy residue fed to the first assembly 402 can be the same ordifferent from the mass ratio fed to the second assembly 404. Bychanging the ratio of oxygen to the recycled flue gas, the heat releaseprofile at different portions of the windbox 208 can be varied.

In an embodiment, the system used for the combustion of oil heavyresidues may use concentric firing system (CFS) compartments whichincrease the oxidizing environment at the waterwall, thereby reducingcorrosion potential. FIG. 6 depicts one such embodiment. In thisembodiment, the combined stream 360B of the FIG. 4 (or 320B in the FIG.3) is directed through a concentric firing nozzle system that is angledtowards the walls (i.e., the waterwalls) of the furnace rather thantowards the center of the furnace. The effect of this angular adjustmentof the nozzles is enhanced by supplying enriched oxygen concentrationsas part of the stream 360B through the nozzles. The enriched oxygenconcentrations in the streams through the concentric firing system (CFS)compartments increase the oxidizing environment at the waterwall therebyreducing corrosion potential.

FIG. 6 illustrates CFS nozzles 506 that are adjusted to direct thestream 360B away from the center fireball circle 504 more toward thewaterwalls 508 of the boiler 502. Enriching the oxygen in thisconcentric firing system flow increases the oxygen concentration nearthe waterwalls 508. This is particularly valuable for high sulfur, highnitrogen content oil heavy residues, where the nozzle angles could bestaged more aggressively for NOx control while controlling corrosivebehavior as well.

Enrichment of oxygen concentrations in the stream 360B requires theselection of a appropriate materials for use in nozzle components thatcontact the stream 360B (see FIG. 4). Appropriate materials such asstainless steel (SS 304, SS 316, and the like) are desirable for use inthe windbox compartments, and other components exposed to heated (>300°F.) oxygen streams that have oxygen concentrations of greater than 23.5wt %, based on the total weight of the stream. In certain embodiments,material savings can be achieved by restricting the oxygen flow in aseparate conduit through the windbox compartment to the existing nozzlesinto the furnace.

FIG. 7 depicts a nozzle 600 for transporting highly concentrated oxygenstreams through the concentric firing system of FIG. 6. As showntherein, the nozzle 600 includes an outer wall 602 that houses a conduit604 for transporting the stream 360B that may contain amounts of oxygenin amounts of greater than 23 wt % (based on the total weight of thestream 360B) into the windbox 208 (see FIGS. 3 and 4) of the boiler. Inan embodiment, only the conduit 604 that is exposed to nearly pureoxygen would need to be of higher grade, oxygen compatible material, andthe other windbox compartments could remain constructed usingconventional air-fired design and materials. In an embodiment, aconcentric conduit 606 may be used for transporting the oil heavyresidues.

Referring once again to FIG. 4, in one embodiment, the combined stream360 and the second oxidant stream 370 may be introduced into the boiler200 at the upper overfired oxidant compartment 204 or at the loweroverfired oxidant compartment 206. The enrichment with oxygen can thustake place in the upper overfired oxidant compartment 204 relative tothe lower overfired oxidant compartment 206, the windbox 208 and/or thehopper zone 210. In another embodiment, the enrichment with oxygen cantake place in the lower overfired oxidant compartment 206 relative tothe upper overfired oxidant compartment 204, the windbox 208 and/or thehopper zone 210. Referring to FIG. 4, one embodiment where the combinedstream 360 and the secondary oxidant stream 370 is introduced into theupper or lower overfired oxidant compartment 204 or 206 respectively.The upper overfired oxidant compartment 204 is closest to the horizontalboiler outlet plane 304, while the lower overfired compartment 206 isthe compartment farthest from the horizontal boiler outlet plane 304.

When the combined stream 360 is introduced into the lower overfiredoxidant compartment 206, the second oxidant stream 370 is introducedinto the upper overfired oxidant compartment 204 and vice versa. Byintroducing the combined stream 360 into the lower overfired oxidantcompartment 206, the oxidant stream in the lower overfired oxidantcompartment 206 is enriched in oxygen relative to the upper overfiredoxidant compartment 204, the windbox 208 and the inlet header zone 210.

Sufficient oxygen is used in the overfired oxidant compartments so thatthe combustion process may continue from the lower boiler while allowingfor the lower boiler to operate at a ratio of oxygen to fuel lower thanthe stoichiometric ratio than the combustion process requires. Thepurpose of enriching the flue gas stream to the overfired oxidantcompartments is to control the amount of nitrogen oxides (NOx) formed aswell as to control the temperatures in the lower furnace.

Referring to FIG. 4, another embodiment related to varying oxygenconcentrations in the upper and lower overfire oxidant compartments 204and 206 is illustrated. The oxygen concentration of the upper overfiredoxidant compartment 204 can be depleted relative to the bulk of thesecond oxidant stream 370 by the introduction of a supplemental flue gasrecirculation stream 380 to the upper overfired oxidant compartment 204.Furthermore, depletion of the upper overfired oxidant compartment 204relative to the bulk of the secondary oxidant stream 370 may beaccomplished by introducing the combined stream 360 into the loweroverfired oxidant compartment 206 and/or the windbox 208. In oneembodiment, the second oxidant stream 370 can be introduced into thewindbox 208, while the supplemental flue gas recirculation stream 380 isfed to the upper overfired oxidant compartment 204.

Upper overfire oxidant compartments depleted in oxygen relative to theglobal oxygen concentration (i.e., 15 to 40 wt %) will allow for highercombustion temperatures and result in higher heat transfer rates in thelower portions of the boiler where there is a lower working fluidtemperature, while decreasing the combustion temperature and resultantheat transfer rates higher in the boiler.

Due to the energy required to increase the temperature of the upperoverfire oxidant, the temperature of the combustion gases will decrease(most of the combustion will have been completed). At a decreasedtemperature of the combustion gases, the resultant flux to the boilerwalls in the portion of the boiler closest to the outlet plane willdecrease. The resulting alteration in the heat transfer profile will bebeneficial for waterwall materials, in particular for supercriticalsteam generators. The primary benefit is to reduce the heat transfer inthe boiler close to the boiler outlet plane where the working fluidtemperatures are highest.

The use of the additional oxygen in the combustion of oil heavy residueshas a number of advantages. Adding oxygen to the oxidant stream locatedbelow the lowest burner assembly alters the heat absorption profile inthe boiler. The ability to alter and control the heat absorption profilecan increase utilization of heat transfer surfaces located in the lowerboiler. This allows for more total heat absorption in the radiantsection of the boiler. This could also reduce peak temperatures and heattransfer rates which generally occur above the windbox, and therebyreduce material requirements and the potential for ash slaggingproblems.

Altering the heat release profile in the boiler can decrease peak boilermaterial temperatures at a constant thermal heat input and the flue gasrecirculation rate. The advantage is that flue gas recirculation ratescan be lowered without peak heat fluxes that causes slagging problemsand/or waterwall tube overheating. Another beneficial result of alteringof the heat release profile in the boiler is to allow for a moreefficient utilization of the heat transfer surface. The benefits for aretrofit boiler is an increase in thermal heat input and thus workingfluid power, while for a new boiler it results in a decrease in boilersize.

A further beneficial result is an improvement in emissioncharacteristics, including carbon monoxide emissions, excess oxygenrequired, unburned carbon, and mineral matter properties. Another resultis a beneficial impact on ash fouling properties in the convectivesection of the boiler, by controlling the boiler outlet temperature. Yetanother advantageous result is a beneficial impact on ash slaggingproperties in the lower section of the boiler. Another benefit is thatductwork used in the first combined streams 360 to the boiler do notneed to tolerate increased oxygen concentrations. The benefit being thatductwork can be constructed from a wider variety of materials therebydecreasing cost. Only the shorter ductwork containing the secondcombined streams 360A, and the like, need tolerate higher oxygenconcentrations after mixing with the second oxidant stream 370. Anotherbenefit for retrofit applications is utilizing existing plant ductwork.

The control systems 290, 291 of the present invention may be an openloop system, whereby fluid flow control devices are adjusted or set atpredetermined settings or set by an operator, or may be a closed loopsystem. As a closed loop system, the fluid flow control devices may beadjusted or set in response to an operation and/or conditional parameterof the boiler and/or boiler island. For example, the fluid flow controldevices may control the fluid flow in response to thermal parameters ofthe boiler or boiler island such as steam temperature, boilertemperature, or other thermal zones of the boiler or boiler island.Similarly the fluid flow control devices may control fluid flow inresponse operational parameters such as system load or changes to theload of the boiler or boiler island. The present invention contemplatesthat a processor or DCS may provide a respective control signal to arespective fluid flow control device in response to a sensed inputsignal, such as an operational or system condition parameter.

FIG. 8 illustrates an example of the carbon heat loss that can beachieved by varying the oxygen content in the stream 360B. The testswere conducted in a 15 MW pilot plant. The tests were conducted using anoxygen stoichiometry of 1 and 0.85 respectively in the fuel compartment(the windbox 208—see FIG. 4). A test was also conducted using air-firedasphalt (the oil heavy residue). As shown therein, improved carbonburnout/carbon heat loss with oxygen enrichment in the fuel compartmentduring 15 MW testing was achieved. Significant improvement in carbonheat loss is achieved by increasing the concentration of oxygen in theoxidant flow through the fuel compartment from 25% to 30%. Control ofthe oxygen concentration and total flow of oxygen into the fuelcompartment is a therefore a useful aspect in optimizing thermalperformance when oil heavy residues are used as fuels.

The enrichment of oxygen in the oxidant to the fuel compartment alsoimpacts heat release and heat absorption in the furnace waterwalls. FIG.9 is a graph that illustrates the impact of oxygen enrichment on heatflux to the furnace wall near the burner/windbox during 15 MW testing.The system controls the oxygen concentrations and distribution ofoxidant along the height of the windbox allowing for adjustment of theheat flux profile in the furnace walls. This is done in concert with theoxygen concentration and oxygen flows to the OFA locations to optimizeoverall furnace waterwall heat flux while maintaining desired combustionefficiency and emission levels. Further adjustment of this oxygendistribution can provide an active control of superheat reheat steamtemperature by shifting furnace waterwall heat absorption and convectivesection absorption.

In an embodiment, a method of controlling the operation of an oxy-firedboiler is provided. The method includes combusting a fuel that comprisesoil heavy residues in a boiler, the oil heavy residues includinghydrocarbon molecules having a number average molecular weight fromapproximately 200 to approximately 3000 grams per mole, discharging fluegas from the boiler, recycling a portion of the flue gas to the boiler,combining a first oxidant stream with the recycled flue gas to form acombined stream, splitting the combined stream into a plurality ofindependent split streams, introducing each independent split stream ata different elevation of the boiler, and controlling independently aparameter of each of the independent split streams to adjust the heatrelease at each respective elevation of the boiler to vary the heatrelease profile of the boiler by adding a second oxidant stream to eachrespective independent split stream to form respective independentoxygen enriched split streams. In an embodiment, the oil heavy residuescomprise asphaltene. In an embodiment, the boiler is a tangentiallyfired boiler. In an embodiment, the step of controlling independentlythe parameter of each independent split stream further includes changinga heat absorption in the boiler to a desired heat absorption pattern. Inan embodiment, at least one of the split streams is introduced into theboiler at a hopper zone located below a windbox, at the windbox and/orin an overfire compartment located above the windbox. In an embodiment,at least a portion of the combined stream is introduced into the boilerin a lower portion of the windbox. In an embodiment, the at least onesplit stream that is introduced into the boiler at the windbox is about50 to about 100 weight percent of the combined stream. In an embodiment,the at least one split stream is introduced into the boiler in a lowerportion of an overfire compartment. In an embodiment, the at least onesplit stream is introduced into the boiler in an upper portion of anoverfire compartment.

In another embodiment, a method is provided. The method includes thesteps of combusting a fuel that comprises oil heavy residues in aboiler, where the oil heavy residues that comprise hydrocarbon moleculeshaving a number average molecular weight from 200 to 3000 grams permole, discharging flue gas from the boiler, recycling a portion of theflue gas to the boiler, combining a first oxidant stream with therecycled flue gases to form a first combined stream, splitting the firstcombined stream into a plurality of independent split streams, combininga second oxidant stream to each respective independent split streamprovided to the boiler to form respective independent oxygen enrichedsplit streams, introducing each independent oxygen enriched split streamto a different elevation of the boiler, and controlling independentlythe amount of the second oxidant stream added to each respectiveindependent split stream to adjust the heat release at each respectiveelevation of the boiler to vary the heat release profile of the boiler.The first combined stream, the independent split streams, and theindependent oxygen enriched split streams do not carry the fuel for theboiler. In an embodiment, the boiler is a tangentially fired boiler. Inan embodiment, adding the second oxidant stream to form the respectiveoxygen enriched split streams is conducted at a position proximate to apoint of entry into the boiler. In an embodiment, the respective splitstreams are sequentially introduced into the boiler. In an embodiment,at least one respective oxygen enriched split stream is introduced intothe boiler at a hopper zone located below a windbox. In an embodiment,the oxygen enriched split stream introduced into the boiler at thewindbox comprises about 50 to about 100 wt % oxygen, based on the totalweight of the stream. In an embodiment, each oxygen enriched splitstream is introduced into the boiler via an annular space disposedaround an inner port, where the inner port introduces the fuel andtransport air into the boiler. In an embodiment, the boiler is a wallfired boiler. In an embodiment, the step of controlling independentlythe parameter of each respective oxygen enriched split stream introducedto the boiler changes the heat pattern of the boiler. In an embodiment,at least one respective oxygen enriched split stream is introduced intothe boiler at an overfire compartment at the hopper zone, wherein theoxygen enriched split stream introduced into the overfire compartment atthe hopper zone comprises up to 50 wt % oxygen based on the total weightof the oxygen enriched split stream.

In yet another embodiment, a system is provided. The system includes anair separation unit, a boiler configured to combust oil heavy residues,the oil heavy residues comprising hydrocarbon molecules having a numberaverage molecular weight from 200 to 3000 grams per mole, a pollutioncontrol system, a gas processing unit and a control system. The airseparation unit is upstream of the boiler, the pollution control systemand the gas processing unit. The boiler is upstream of the pollutioncontrol system and the gas processing unit. Flue gas is recycled fromthe gas processing unit to the boiler via the air separation unit. Thecontrol system is configured to control the addition of a first oxidantstream to the recycled flue gas to form a combined stream and to controlthe addition of a second oxidant stream to a plurality of independentsplit streams formed from the combined stream to vary the heat releaseprofile of the boiler. Each of the independent split streams to whichthe second oxidant stream is added is introduced to a differentelevation of the boiler.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty

This written description uses examples to disclose several embodimentsof the invention, including the best mode, and also to enable one ofordinary skill in the art to practice the embodiments of invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the invention is definedby the claims, and may include other examples that occur to one ofordinary skill in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

What is claimed is:
 1. A method of controlling the operation of anoxy-fired boiler, the method comprising: combusting a fuel thatcomprises oil heavy residues in a boiler, the oil heavy residuesincluding hydrocarbon molecules having a number average molecular weightfrom approximately 200 to approximately 3000 grams per mole; dischargingflue gas from the boiler; recycling a portion of the flue gas to theboiler; combining a first oxidant stream with the recycled flue gas toform a combined stream; splitting the combined stream into a pluralityof independent split streams; introducing each independent split streamat a different elevation of the boiler; and controlling independently aparameter of each of the independent split streams to adjust the heatrelease at each respective elevation of the boiler to vary the heatrelease profile of the boiler by adding a second oxidant stream to eachrespective independent split stream to form respective independentoxygen enriched split streams.
 2. The method according to claim 1,wherein: the oil heavy residues comprise asphaltene.
 3. The methodaccording to claim 1, wherein: the boiler is a tangentially firedboiler.
 4. The method according to claim 1, wherein: controllingindependently the parameter of each independent split stream furtherincludes changing a heat absorption in the boiler to a desired heatabsorption pattern.
 5. The method according to claim 1, wherein: atleast one of the split streams is introduced into the boiler at a hopperzone located below a windbox, at the windbox and/or in an overfirecompartment located above the windbox.
 6. The method according to claim1, wherein: at least a portion of the combined stream is introduced intothe boiler in a lower portion of the windbox.
 7. The method according toclaim 6, wherein: the at least one split stream that is introduced intothe boiler at the windbox is about 50 to about 100 weight percent of thecombined stream.
 8. The method according to claim 1, wherein: the atleast one split stream is introduced into the boiler in a lower portionof an overfire compartment.
 9. The method according to claim 1, wherein:the at least one split stream is introduced into the boiler in an upperportion of an overfire compartment.
 10. A method comprising: combustinga fuel that comprises oil heavy residues in a boiler, where the oilheavy residues that comprise hydrocarbon molecules having a numberaverage molecular weight from 200 to 3000 grams per mole; dischargingflue gas from the boiler; recycling a portion of the flue gas to theboiler; combining a first oxidant stream with the recycled flue gases toform a first combined stream; splitting the first combined stream into aplurality of independent split streams; combining a second oxidantstream to each respective independent split stream provided to theboiler to form respective independent oxygen enriched split streams;introducing each independent oxygen enriched split stream to a differentelevation of the boiler; and controlling independently the amount of thesecond oxidant stream added to each respective independent split streamto adjust the heat release at each respective elevation of the boiler tovary the heat release profile of the boiler; wherein the first combinedstream, the independent split streams, and the independent oxygenenriched split streams do not carry the fuel for the boiler.
 11. Themethod according to claim 10, wherein: the boiler is a tangentiallyfired boiler.
 12. The method according to claim 10, wherein: adding thesecond oxidant stream to form the respective oxygen enriched splitstreams is conducted at a position proximate to a point of entry intothe boiler.
 13. The method according to claim 10, wherein: therespective split streams are sequentially introduced into the boiler.14. The method according to claim 10, wherein: at least one respectiveoxygen enriched split stream is introduced into the boiler at a hopperzone located below a windbox.
 15. The method according to claim 14,wherein: the oxygen enriched split stream introduced into the boiler atthe windbox comprises about 50 to about 100 wt % oxygen, based on thetotal weight of the stream.
 16. The method according to claim 14,wherein: each oxygen enriched split stream is introduced into the boilervia an annular space disposed around an inner port, where the inner portintroduces the fuel and transport air into the boiler.
 17. The methodaccording to claim 10, wherein: the boiler is a wall fired boiler. 18.The method according to claim 10, wherein: controlling independently theparameter of each respective oxygen enriched split stream introduced tothe boiler changes the heat pattern of the boiler.
 19. The methodaccording to claim 14, wherein: at least one respective oxygen enrichedsplit stream is introduced into the boiler at an overfire compartment atthe hopper zone; and wherein the oxygen enriched split stream introducedinto the overfire compartment at the hopper zone comprises up to 50 wt %oxygen based on the total weight of the oxygen enriched split stream.20. A system comprising: an air separation unit; a boiler configured tocombust oil heavy residues, the oil heavy residues comprisinghydrocarbon molecules having a number average molecular weight from 200to 3000 grams per mole; a pollution control system; a gas processingunit, wherein the air separation unit is upstream of the boiler, thepollution control system and the gas processing unit, wherein the boileris upstream of the pollution control system and the gas processing unit,and wherein flue gas is recycled from the gas processing unit to theboiler via the air separation unit; and a control system configured tocontrol the addition of a first oxidant stream to the recycled flue gasto form a combined stream and to control the addition of a secondoxidant stream to a plurality of independent split streams formed fromthe combined stream to vary the heat release profile of the boiler;wherein each of the independent split streams to which the secondoxidant stream is added is introduced to a different elevation of theboiler.